EORAMINIFERA OF THE COAL. 
437 
vestigation of other countries has led to quite a different re¬ 
sult. Thus, near Clifton, on the Avon, as well as at numer¬ 
ous places around the Bristol basin from the Mendip Hills 
to Tortworth, there is a celebrated bone-bed,” almost en- 
491 . tirely made up of icli- 
thyolites. It occurs at 
the base of the Lower 
Limestone shales im¬ 
mediately resting upon 
the passage beds of 
the Old Red Sandstone. 
Psammodus porosus, Agass. Bone-bed, Mountain Similar bonc - bcds OC- 
Limestone. Bristol, Armagh. Carboniferous 
Limestone of Armagh, in Ireland, where they are made up 
chiefly of the teeth of fishes of the Placoid order, nearly all 
of them rolled as if drifted 
from a distance. Some teeth 
are sharp and pointed, as in 
ordinary sharks, of which the 
genus Cladodus affords an il¬ 
lustration; but the majority, 
as in Psammodus and Cochli- 
odus^ are, like the teeth of the 
Cestracion of Port Jackson 
(see above. Fig. 261, p. 297), 
massive palatal teeth fitted for 
grinding. (See Figs. 491,492.) 
There are upward of seventy other species of fossil fish 
known in the Mountain Limestone of the British Islands. 
The defensive fin-bones of these creatures are not unfrequent 
at Armagh and Bristol; those known .Or acanthus^ Cteno- 
cantlius.^ and OncJms are often of a very large size. Ganoid 
fish, such as Holoptychins., also occur; but these are far less 
numerous. The great Megalichthys Ilibberti appears to 
range from the Upper Coal-measures to the lowest Carbonif¬ 
erous strata. 
Poraminifera. —In the upper part of the Mountain Lime¬ 
stone group in the S. W. of England, near Bristol, limestones 
having a distinct oolitic structure alternate with shales. In 
these rocks the nucleus of every minute spherule is seen, un¬ 
der the microscope, to consist of a small rhizopod or forami- 
nifer. This division of the lower animals, which is repre¬ 
sented so fully at later epochs by the l^ummulites and their 
numerous minute allies, appears in the Mountain Limestone to 
be restricted to a very few species, among which Textularia.^ 
Nodosaria.^ Midothyra^^ndi Ftisulina (Fig. 493),have been rec- 
Fig. 492. 
Cochliodus contort 2 is, Agnss. Boii e-bed. 
Mountain Limestone. Bristol, Armagh. 
